Recently, the traffic of wireless communications has largely increased. However, since the frequency bands used in the wireless communications are finite, the improvement of the use efficiency of frequencies is demanded. To improve the use efficiency of frequencies, for example, an idle mode is adopted in a long term evolution (LTE), a worldwide interoperability for microwave access (WiMAX), etc.
FIG. 1 is an example of a configuration of a wireless frame used in the communication between a base station and a mobile terminal on a plane expressed by a frequency and time. The frame illustrated in FIG. 1 includes an area 101 (101a, 101b) used in the transmission and reception of control data, and a data area 102 used in the transmission and reception of user data. The data area 102 is not assigned to a mobile terminal which transmits or receives no user data. However, although no user data is transmitted or received, a mobile terminal in an active state transmits and receives control data with a base station. Therefore, it is assigned a frequency band used in transmitting and receiving control data as, for example, illustrated by 103a through 103f. 
When an idle mode is set, a mobile terminal does not transmit or receive control data with a base station. In this case, since the frequency band assigned to the mobile terminal set in the idle mode is released, the released frequency band is assigned to another mobile terminal, thereby increasing the number of communicatable mobile terminals.
Described next is an example of a method of setting an idle mode. When a base station detects that no user data is transmitted or received in a mobile terminal, it activates a timer for monitoring a no communication status, and monitors whether or not user data is transmitted or received before the timeout of the timer. Unless the transmission and reception of user data are resumed before the timeout of the timer, the base station transmits a disconnection request (instruction to set the idle mode) to the mobile terminal. After transmitting the disconnection request, the base station releases the frequency band which has been assigned to the mobile terminal in the period in which has been assigned to the mobile terminal receiving the disconnection request. On the other hand, when the transmission and reception of the user data to and from the mobile terminal which is set in the idle mode are started, the base station performs a connecting process with the mobile terminal in which the transmission and reception of the user data have been resumed, and assigns a frequency band to the mobile terminal.
As related technology a communication system for storing the history of requested traffic from the past to the present and the history of the communication disconnection by a timeout, and predicting the communication status in the future based on the history of requested traffic is known. In this system, the time interval up to a timeout is calculated from the communication status in the future.